1. Field of the Invention
The invention relates to a storage vessel for a liquid, the storage vessel having an arrangement for measuring the electrical conductivity of the liquid that is located in the storage vessel, and a method for this purpose.
2. Related Art
Storage vessels for aqueous urea solutions are known. Known storage vessels comprise measuring devices, with which the electrical conductivity of the liquid that is located in the storage vessel is conductively measured. Aqueous urea solution is used, for example, in SCR systems (selective catalytic reduction systems), in order, in a catalytic process, to reduce the proportion of the nitrogen oxide in the exhaust gas from diesel engines. The aging state and/or the quality of the solution can be established by determining the conductivity of the urea solution. Conductivity measurements of the urea solution are also carried out in order to determine the fill level of the liquid in the storage vessel.
In the case of the known storage vessels, at least two electrodes are fed through the housing wall, which electrodes are in conductive contact with the liquid. The sites where these electrodes are fed through are sealed by O-rings in order to prevent liquid escaping from the storage vessel at these sites.
An electrical voltage is applied between the contacts of the storage vessel in order to measure the conductivity. If the liquid is electrically conductive, the contacts are mutually connected by way of the liquid and a current flows between the electrodes due to the electrical field. The strength of the current is representative of the conductivity of the liquid.
Plug systems or detachable cable connections are used in order to produce the electrical connection between the storage vessel and an electronic measuring device. In the case of repair or servicing, these connections are initially detached and eventually re-attached.
The presence of defects in liquid tightness and/or leakages at the feedthroughs of the electrodes is problematic in the case of the known storage vessels, in which leakages and defects in liquid tightness arise, for example, as a result of mechanical loadings. Loadings of this type occur, for example, as a result of vibrations at the installation site of the storage vessel or as a result of detaching the cable connection multiple times.
As these storage vessels are exposed to intensified vibrations and cable movements in SCR systems, material fatigue also becomes a factor in the connection cables, which leads to loose connections or cable breaks.